Cable Fault Tester Working Principle
The working principle of a power cable fault tester: A power cable fault tester consists of three main parts: the main unit, the cable fault locator, and the cable path analyzer. The main unit measures the nature of the cable fault, its total length, and the approximate location of the fault point from the test end. The cable fault locator determines the precise location of the fault point based on the approximate location determined by the main unit. For buried cables with unknown routes, the path analyzer is used to determine the underground route of the cable. The basic method for testing power cable faults is to apply a high-voltage pulse to the faulty power cable, causing a breakdown at the fault point. The discharge at the breakdown point generates electromagnetic waves and emits sound simultaneously.
The working principle of the arc reflection method (secondary pulse method) in cable fault location is as follows: First, a high-voltage pulse of a certain voltage level and energy is applied to the faulty cable at the test end, causing the high-resistance fault point to break down and arc. Simultaneously, a low-voltage pulse for measurement is added at the test end. When the measuring pulse reaches the high-resistance fault point, it encounters the arc and is reflected on the surface of the arc. Because the high-resistance fault becomes an instantaneous short-circuit fault during arcing, the low-voltage measuring pulse undergoes a significant impedance characteristic change, making the flashover measurement waveform a low-voltage pulse short-circuit waveform. This makes waveform identification particularly simple and clear. This is what we call the "secondary pulse method." The low-voltage pulse reflection waveform received by the cable fault tester is equivalent to the waveform of a conductor completely short-circuited to ground. By superimposing the low-voltage pulse waveforms obtained when the high-voltage pulse is released with those obtained when it is not, the two waveforms will have a divergence point, which is the reflected waveform point of the fault point. This method combines the low-voltage pulse method and high-voltage flashover technology, making it easier for testers to determine the location of the fault. Compared with traditional testing methods, the advantage of the secondary pulse method is that it simplifies the complex waveform in the high-voltage flashover method into the simplest low-voltage pulse short-circuit fault waveform, making the interpretation extremely simple and accurately determining the fault distance.
The three-pulse method in cable fault testers employs a dual-impact approach to extend and stabilize the arc, enabling easy location of high-resistance and flashover faults. The three-pulse method is technologically advanced, simple to operate, produces clear waveforms, and provides rapid and accurate location, making it the mainstream method for locating high-resistance and flashover faults. An upgrade from the two-pulse method, the three-pulse method first measures the reflected waveform of a low-voltage pulse without breaking down the fault point in the cable under test. Then, a high-voltage pulse breaks down the fault point to generate an arc. When the arc voltage drops to a certain value, a medium-voltage pulse is triggered to stabilize and extend the arc time. Afterward, a low-voltage pulse is emitted, and the cable fault tester obtains the reflected waveform of the fault point. Superimposing these two waveforms reveals the divergence point, which corresponds to the fault location. Because a medium-voltage pulse is used to stabilize and extend the arc time, it is easier to obtain the fault waveform than the two-pulse method. Compared to the two-pulse method, the three-pulse method is simpler to operate as it does not require selecting the synchronization duration of the arc.
